1. Field of the Invention
The present invention relates to a bookbinding machine which binds sheets of paper having images formed on the top surfaces into a booklet, and a prebinding apparatus which is installed in the bookbinding machine to execute a prebinding process.
2. Description of the Related Art
At a binding state, an image forming process for forming images on top surfaces of sheets of paper using a printing machine, a printer or similar techniques, a prebinding process for cutting edge portions or margins of the sheets of paper having images formed on the top surfaces (hereinafter also called “image-formed sheets of paper”) and creasing the image-formed sheets of paper, and a binding process of stacking and connecting the image-formed sheets of paper, undergone the prebinding process, in the order of pages and folding the image-formed sheets of paper along the creases to provide a booklet are carried out in order. The prebinding process includes a step of cutting off the margins at both sides of sheets of paper (slitter step), a step of cutting top and bottom margins of sheets of paper (cutter step) and a step of creasing (creaser step), which are generically called an SCC (Slitter, Cuter and Creaser) step.
The slitter step and the cutter step are needed to remove margins, which are inevitably produced at the time of printing, when performing, for example, full-size printing. When printing is done on a thick sheet of paper such as color print paper, if the sheet is folded directly in the binding process, cracks may occur at the folded portion. The creaser step is needed to prevent the occurrence of cracking. When an image is formed with sufficient margins provided at the peripheral portion of a sheet of paper, therefore, the image can be formed initially on a sheet of paper of the binding size, thus eliminating the slitter step and the cutter step. The creaser step is unnecessary when an image is formed on a thin sheet of paper and no printing is done at the folded portion as in, for example, monochromatic printing.
There is an off-line type of prebinding apparatus which performs the SCC step; for example, a single sheet type apparatus as disclosed in, for example, Japanese Patent Laid-Open Publication No. 2001-232700. There also is a batch type apparatus. In case of binding full-size color print sheets, an image forming apparatus such as a printer forms images on sheets of paper with an extra size greater than the binding size by printing or so, a worker carries the image-formed sheets from the image forming apparatus to a prebinding apparatus, performs the SCC step using the prebinding apparatus, then carries the image-formed sheets from the prebinding apparatus to a bookbinding apparatus to perform the binding process with the bookbinding apparatus.
The prior art however has the following shortcomings. As the prebinding process is conventionally performed off line, carrying sheets of paper between the image forming apparatus and the prebinding apparatus and between the prebinding apparatus and the bookbinding machine is done by a worker. This slows down the processing speed and leads to a lower efficiency. In addition, the prebinding apparatus and the bookbinding apparatus should be operated individually, resulting in a large operational burden and a lower efficiency.
A prebinding apparatus as described in the Japanese Patent Laid-Open Publication No. 2001-232700 may be coupled to the subsequent stage of the image forming apparatus, and a bookbinding machine may be coupled to the subsequent stage of the prebinding apparatus to assemble an on-line bookbinding machine having those apparatuses coupled in the order of the image forming apparatus—prebinding apparatus—bookbinding apparatus. But, such a bookbinding machine performs the SCC step on all of image-formed sheets of paper output from the image forming apparatus. As mentioned above, however, pages of image-formed sheets of paper printed in full size and pages of thick sheets of paper, such as color print sheets, need the SCC step, while pages of thin sheets of paper with margins at the peripheral portions, such as monochromatic print sheets, do not need the SCC step. Booklets with a mixture of pages of thin sheets with margins at the peripheral portions and pages printed in full size are increasing recently. Even when an on-line bookbinding machine is constructed by a simple combination of conventional apparatuses, the machine performs the SCC step even on sheets of paper which do not require the SCC step. This reduces the bookbinding efficiency to the contrary to the purpose of the on-line machine.